Jun 9, 2011 2000 UTC Day 1 Convective Outlook
Updated: Thu Jun 9 20:04:10 UTC 2011
Probabilistic to Categorical Outlook Conversion Table
Public Severe Weather Outlook

The SPC is forecasting ...severe thunderstorms expected over parts of the northeast us this afternoon....   Please read the latest public statement about this event.

Categorical Graphic
20110609 2000 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20110609 2000 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Probabilistic Damaging Wind Graphic
20110609 2000 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Probabilistic Large Hail Graphic
20110609 2000 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
   SPC AC 092000
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0300 PM CDT THU JUN 09 2011
   
   VALID 092000Z - 101200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS ACROSS PORTIONS OF
   PA/NY/NJ/NH/CT/RI/MA/VT...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE SOUTHERN
   PLAINS/MIDWEST TO NEW ENGLAND...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS EASTERN WY/FAR NORTHEAST
   CO...
   
   ...NORTHEAST STATES/NEW ENGLAND...
   BANDS OF INTENSE THUNDERSTORMS CONTINUE TO MERGE/EXPAND AND GROW
   UPSCALE THIS AFTERNOON WITH A BROAD/WELL-ORGANIZED LINE OF TSTMS NOW
   EVOLVING ACROSS THE NORTHEAST STATES/SOUTHERN NEW ENGLAND. SPECIAL
   16Z/18Z OBSERVED SOUNDINGS REFLECT VERY STRONG INSTABILITY/STEEP
   LAPSE RATES ON THE SOUTHERN FRINGE OF STRONG WESTERLIES ALOFT.
   SCENARIO STILL EXPECTED TO YIELD WIDESPREAD WIND DAMAGE IN ADDITION
   TO BOUTS OF LARGE HAIL AND PERHAPS A BRIEF TORNADO OR TWO. GIVEN
   AMPLE PRE-CONVECTIVE LINE HEATING/SOUTHWESTERLY FLOW...THE PRIMARY
   20Z CHANGE WAS TO EXTEND THE MODERATE RISK EASTWARD ACROSS VIRTUALLY
   ALL OF THE SOUTHERN NEW ENGLAND COAST. PLEASE REFERENCE
   ONGOING/SUBSEQUENT WATCHES AND MESOSCALE DISCUSSIONS.
   
   ...LOWER/MIDDLE MO VALLEY AND MIDWEST/SOUTH-CENTRAL PLAINS...
   PRIOR REASONING GENERALLY HOLDS...ALTHOUGH INTRODUCED SOMEWHAT
   HIGHER TORNADO PROBABILITIES /10 PERCENT/ IN GENERAL VICINITY OF AN
   OUTFLOW-AIDED TRIPLE POINT ACROSS THE LOWER-MIDDLE MO VALLEY.
   REFERENCE MESOSCALE DISCUSSION 1155.
   
   ANOTHER CHANGE WAS TO EXTEND THE SLIGHT RISK SOUTHWESTWARD IN
   VICINITY OF THE DRYLINE ACROSS FAR SOUTHWEST OK INTO PORTIONS OF THE
   EASTERN TX PANHANDLE/NORTHWEST TX. HERE...DAMAGING WINDS/SOME HAIL
   MAY BE A CONCERN LATE THIS AFTERNOON/EARLY EVENING.
   
   ..GUYER.. 06/09/2011
   
   .PREV DISCUSSION... /ISSUED 1129 AM CDT THU JUN 09 2011/
   
   ...SYNOPSIS...
   SUPPRESSION OF THE S CENTRAL AND SERN U.S. UPPER RIDGE IS FORECAST
   TO CONTINUE TODAY...AS THE WRN U.S. TROUGH SHIFTS EWD AND AT THE
   SAME TIME AN ERN CANADA TROUGH MOVES EWD -- FORCING FALLING
   HEIGHTS/CYCLONIC FLOW TO SPREAD ACROSS THE NORTHEAST CONUS.
   
   AT THE SURFACE...COLD FRONT WILL CONTINUE CROSSING THE ST. LAWRENCE
   VALLEY/LOWER GREAT LAKES REGION THIS MORNING...AND WILL BECOME A
   FOCUS FOR WIDESPREAD SEVERE STORM DEVELOPMENT AS IT SHIFTS INTO NEW
   ENGLAND/NY/PA.  THE OUTFLOW-REINFORCED FRONT WILL LINGER WWD ACROSS
   THE OH VALLEY...AND WILL RETREAT NWD WITH TIME ACROSS THE MO VALLEY
   REGION WITH FRONTAL LOW DEVELOPMENT EXPECTED IN THIS AREA IN
   RESPONSE TO EJECTING PIECES OF THE WRN U.S. TROUGH.
   
   ...NEW ENGLAND WSWWD ACROSS THE MIDWEST/OH VALLEY...
   POTENTIALLY WIDESPREAD/DAMAGING WIND EVENT IS FORECAST ACROSS THE
   NORTHEAST U.S. TODAY.  ONGOING CONVECTION ACROSS THIS RISK AREA HAS
   DIMINISHED EARLY THIS MORNING...WITH CONVECTIVE-COOLED AIR OVER SRN
   NEW ENGLAND EXPECTED TO CONTINUE RECOVERING.  AS A LARGE PLUME OF
   VERY STEEP LAPSE RATES ATOP A VERY MOIST /NEAR 70 DEWPOINTS/
   BOUNDARY LAYER COMBINES WITH CLEARING SKIES SUPPORTING STRONG WARM
   SECTOR HEATING...MIXED-LAYER CAPE OF 2000 TO 3000 J/KG IS EXPECTED
   TO DEVELOP QUICKLY THROUGH EARLY AFTERNOON.  AN OUTFLOW BOUNDARY
   INVOF THE MID AND UPPER OH VALLEY -- AND THE COLD FRONT NOW CROSSING
   THE LOWER GREAT LAKES/ST. LAWRENCE VALLEY -- WILL BECOME THE FOCUS
   FOR WIDESPREAD STORM DEVELOPMENT OVER THE NEXT COUPLE OF
   HOURS...SHIFTING SEWD WITH TIME ACROSS NY/PA/OH AND MUCH OF NEW
   ENGLAND.
   
   WITH STRONGEST DEEP-LAYER WLYS PROGGED TO REMAIN N OF THE
   MASON/DIXON LINE...MOST WIDESPREAD SEVERE THREAT APPEARS TO EXIST
   FROM SWRN PA ENEWD ACROSS SRN AND ERN NY INTO SRN NEW ENGLAND. 
   HERE...VERY LARGE HAIL THREAT WITH INITIAL SUPERCELL STORMS SHOULD
   EVOLVE INTO MORE OF A DAMAGING WIND THREAT AS CONVECTION EVOLVES
   INTO ONE OR MORE BOWING LINES WHICH WILL MOVE QUICKLY EWD.  A COUPLE
   OF TORNADOES MAY ALSO OCCUR -- PARTICULARLY EARLY ON WITH MORE
   ISOLATED STORMS. 
   
   BY THIS EVENING...CONVECTION WILL HAVE SHIFTED WELL SEWD...FROM SRN
   AND ERN NEW ENGLAND WSWWD INTO NRN VA/WV.  WITH WEAKER FLOW S OF THE
   MASON/DIXON LINE...MORE ISOLATED SEVERE POTENTIAL IS FORECAST.  
   
   ...MID MO VALLEY REGION AND VICINITY SWWD INTO NRN OK...
   COMPLEX SCENARIO EXISTS ACROSS THE CENTRAL PLAINS/MID MO VALLEY
   REGION...AS EARLY MORNING SHORT-WAVE RIDGING ALOFT IS FORECAST TO
   CONTINUE WEAKENING AS TROUGHING SHIFTS ENEWD.  AS SURFACE LOW
   REDEVELOPS NWD INTO THE MID MO VALLEY REGION IN RESPONSE TO THE
   APPROACHING TROUGH...AND THE SURFACE FRONT OVER NRN MO RETREATS NWD
   INTO IA...STORM DEVELOPMENT WILL OCCUR -- SUPPORTED BY MODERATE TO
   STRONG WARM SECTOR DESTABILIZATION.  
   
   WITH BACKING/STRENGTHENING LOW-LEVEL FLOW INVOF THE DEVELOPING
   LOW/WARM FRONT BENEATH 50 KT SWLYS AT MID LEVELS SPREADING ATOP THIS
   AREA...SHEAR/INSTABILITY COMBINATION WILL BE QUITE SUPPORTIVE OF
   SUPERCELLS.  ALONG WITH THREAT FOR VERY LARGE HAIL...ISOLATED
   TORNADOES WILL ALSO BE POSSIBLE -- MAINLY FROM SERN NEB/NERN KS EWD
   INTO NRN MO/SRN IA.  LOCALLY DAMAGING WINDS WILL ALSO BE
   POSSIBLE...POSSIBLY BECOMING MORE LIKELY WITH TIME AS SOME
   CLUSTERING OF CONVECTION OCCURS INTO THE EVENING HOURS.
   
   MORE ISOLATED STORM DEVELOPMENT IS FORECAST TO OCCUR SWD ACROSS
   CENTRAL/ERN KS AND INTO OK...NEAR AND AHEAD OF THE SURFACE COLD
   FRONT.  ALONG WITH POTENTIAL FOR HAIL...DEEP/DRY SUB-CLOUD MIXED
   LAYER WILL SUPPORT EVAPORATIVELY-ENHANCED DOWNDRAFTS -- AND THUS
   SOME LIKELIHOOD FOR LOCALLY DAMAGING GUSTS.
   
   ...ERN WY AND VICINITY...
   DESPITE FAIRLY EXTENSIVE MORNING CLOUD COVER...SOME DESTABILIZATION
   WILL SUPPORT AFTERNOON STORM DEVELOPMENT -- INITIALLY OVER THE
   HIGHER TERRAIN BUT THEN SPREADING EWD INTO LOWER ELEVATIONS.  WITH
   STRONG /50 TO 60 KT/ MID-LEVEL WLY JET STREAK SHIFTING ACROSS THIS
   REGION...SHEAR WILL SUPPORT ORGANIZED/SUPERCELL STORMS...AND THUS --
   DESPITE POSSIBLY LIMITED INSTABILITY IN PARTS OF THE AREA --
   CONTINUATION OF SLIGHT RISK FOR HAIL IS WARRANTED.  MORE ISOLATED
   THREAT APPEARS TO EXTEND SWD INTO THE CO FRONT RANGE AREA...AS
   SUBSIDENCE EVIDENT IN THE WAKE OF A SEPARATE/DEPARTING SHORT-WAVE
   TROUGH SHOULD LIMIT COVERAGE A BIT WITH SWD EXTENT.
   
   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z